Mean survival time of patients with Cystic Fibrosis (CF) has increased and osteopenia, osteoporosis and pathologic fractures have been reported with increasing frequency as early as the first decade of life. We will evaluate children with CF and their status of bone mineralization in relation to their stage of pubertal development. Patients with delayed puberty will receive gonadal steroid replacement therapy and we expect to find significant improvement in their bone mineralization after 6 months of therapy.